1. Field of the Invention
The invention relates to an injection device for injecting a selectable dose of a liquid substance from an ampoule located in an ampoule holder, comprising a sleeve-shaped mechanism holder mechanically coupled thereto, in the interior of the mechanism holder a longitudinally shiftable shaft with a piston disposed thereon being provided which acts on the ampoule, wherein the shaft being surrounded by an also longitudinally shiftable advancing sleeve, mechanically coupled thereto, which in its upper end area is closed by a lid.
2. Description of the Prior Art
An advancing facility for an injection device is known from EP 0 627 229 A1 by means of which a liquid substance from an ampoule can be administered. This advancing device consists of an outer sleeve, an inner sleeve protruding backward from the outer sleeve, and a toothed shaft movable by means of the inner sleeve against the force of a spring. The toothed shaft is provided with teeth, the length of which corresponds to a full injection dose. The inner sleeve is movable forward and backward by the value of the length of a full injection dose between two stops provided on the outer sleeve. The inner sleeve is provided with catching means which lock it in place upon reaching the front position at an opening of the carpoule sleeve, in an unlocking manner with respect to this. Finally, a recoil protection is intended for the toothed shaft.
The injection device provided with this advancing device cannot be employed once more after emptying the carpoule or ampoule.
Another injection device of this kind is known from EP 0 373 321 B1 which consists of an ampoule sleeve for receiving the ampoule and a delivering mechanism. In turn, this is composed of a cylindrical piston shaft with an inner hollow cylinder and an outer hollow cylinder which is formed in one piece with this and that exhibits a guiding cam on its outer shell. A dosing ring is fixed radially to the outer hollow cylinder. The dosing can be read off by means of a scaling fastened to the outer perimeter of the dosing ring through a sight glass set into the housing of the mechanism holder. The delivering mechanism is longitudinally movably arranged in the mechanism holder by means of a retaining spring and secured by a lid screwable into the housing of the mechanism holder. The dosing ring rests against the lid with the force of the retaining spring. The housing of the mechanism holder is provided on its inside with elongated slots of different length in which the corresponding guiding cam of the delivering mechanism is able to glide. As a result, the lift of the delivering mechanism is determined by the length of the elongated slot combining with the guiding cam. The adaptation to the needs of the patients of the dose to be administered exclusively takes place by an authorized person, e.g. a physician. A special-purpose tool is necessary, by means of which an interlocking ring of the device can be unlocked until the guiding cam of the delivering mechanism is released from the respective elongated slot. The physician is then able to select the desired dose by rotation of the released delivering mechanism and renewed catch of the guiding cam into a corresponding elongated slot.
Once selected, the dose cannot be varied without considerable effort. In addition, based on the construction of the delivering mechanism, the injection device can only be used for delivering a single dose although possibly a sufficient supply of medicine is still available in the ampoule. In order to administer another dose of medicine, the ampoule sleeve must be unlocked from the mechanism holder and disposed of together with the ampoule possibly still containing medicine.
An injection device of generic type is known from EP 0 037 696 B1 with which a dose of a liquid substance to be administered can be taken from an ampoule via a transmission mechanism of tractive force effective in one direction upon operating a locking cap. The transmission mechanism of tractive force consists in that one pushing part is equipped with a plurality of teeth and the other pushing part with a pawl, which intermesh and therefore effect the advance of the transmission mechanism of tractive force only in one direction. The maximum lift height and therefore the maximum dose to be administered is limited via a notch and a stop. The operator of the injection device is also able to select less than the maximum dose by listening to the number of clicks which occur when, during the advance, the teeth of the pushing part catch in the pawl. In this connection, one click corresponds to the minimum dose. The operating element, the locking cap, is pushed back up to a stop by means of a spring.
This injection device is designed for extremely careful operation since a click can easily be misheard and different doses to be administered not be safely adjusted. In addition, no display unit is foreseen for the dose to be selected.
Furthermore, the basic problem of these and other injection devices of generic type is that, according to the dose selection, when so to say the last drop which does not correspond to a full dose is still available in the ampoule, this supply is no longer sufficient to fully administer the adjusted dose. Up to now, the operator had no instrument to recognize that this dose, adjusted by him, cannot completely be administered anymore and possibly injected himself with an underdose with serious health consequences.